Regulation of the Expression of GARP/Latent TGF-b1 Complexes on Mouse T Cells and Their Role in Regulatory T Cell and Th17 Differentiation

May 03, 2013

Edwards et al. 2013, Journal of Immunology

GARP/LRRC32 was defined as a marker of activated human regulatory T cells (Tregs) that is responsible for surface localization of latent TGF-b1. We find that GARP and latent TGF-b1 are also found on mouse Tregs activated via TCR stimulation; however, in contrast to human Tregs, GARP is also expressed at a low level on resting Tregs. The expression of GARP can be upregulated on mouse Tregs by IL-2 or IL-4 exposure in the absence of TCR signaling. GARP is expressed at a low level on Tregs within the thymus, and Treg precursors from the thymus concomitantly express GARP and Foxp3 upon exposure to IL-2. The expression of GARP is independent of TGF-b1 and TGF-b1 loading into GARP and is independent of furin-mediated processing of pro–TGFb1 to latent TGF-b1. Specific deletion of GARP in CD4+ T cells results in lack of expression of latent TGF-b1 on activated Tregs. GARP-deficient Tregs develop normally, are present in normal numbers in peripheral tissues, and are fully competent suppressors of the activation of conventional T cells in vitro. Activated Tregs expressing GARP/latent TGF-b1 complexes are potent inducers of Th17 differentiation in the presence of exogenous IL-6 and inducers of Treg in the presence of IL-2. Induction of both Th17- producing cells and Tregs is caused preferentially by Tregs expressing the latent TGF-b1/GARP complex on their cell surface rather than by secreted latent TGF-b1.

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